1. Field of the Invention
This invention relates to a catalyst for use in water treatment and to a method for the water treatment by the use of the catalyst. More particularly, this invention relates to a water-treating catalyst to be used in the treatment of water with ozone for deodoring, sterilization and decoloring treatment, a water-treating catalyst to be used for the decomposition and removal of ozone remaining in the water resulting from the water treatment with ozone, and a method for the water treatment by the use of the catalyst mentioned above.
2. Description of the Prior Art
The treatment of ozonization is widely used for oxidative decomposition and removal of harmful components, odorous component, coloring components, etc. from water. It is specifically utilized in treating waste water or service water for the purpose of deodorization, sterilization, and decolorization. Particularly, in recent years, the treatment of ozonization has been gaining in significance in the light of the problem of pollution of water with trihalomethane, the problem of leakage of odorous pollutant in service water due to the degradation of quality of water entering the water supply system, and the necessity for high-degree treatment due to fortification of the regulation on disposal of waste water. When the treatment is performed solely with ozone, however, the speed of oxidation of the hostile components is slow and the efficiency of removal of the components is low. As a remedy for the imperfection of this treatment, a method for combining the treatment of ozonization and the treatment with ultraviolet light has been proposed (Japanese Patent Laid-Open SHO 63(1988)-72,396). Though this method enhances the efficiency of removal of hostile components, it suffers from the disadvantage that the speed of treatment is slow and the equipment for the treatment is complicate. A catalyst has been proposed (WO 81/02887) which is used in the treatment of ozonization for the purpose of enhancing the efficiency of removal of hostile component with ozone. It is not fully satisfactory, however, in terms of the speed of treatment and the durability.
The ozone dissolved in water is decomposed relatively quickly in the alkaline zone. In the neutral to acid zone, however, it is decomposed slowly and takes up much time for decomposition. The residual ozone which survives the decomposition poses a problem. Where the treatment of ozonization is followed by a treatment with chlorine, for example, there ensures a demerit that the residual ozone entails an increase in the amount of chlorine used for the treatment. Where the treatment of ozonization is followed by a treatment with activated carbon, there arises the problem that the residual ozone consumes the activated carbon in the form of oxidation. The prevention of these problems necessitates removal of the residual ozone. Few techniques have ever been developed for effecting this removal of the residual ozone. Among the methods resorting to use of a catalyst is counted a method which uses a filter material layer provided with a manganese dioxide catalyst surface (Japanese Patent Laid-Open SHO 59(1984)-139,991).
An object of this invention, therefore, is to provide a catalyst for use in water treatment which exhibits a highly satisfactory performance in such treatments for water as aimed at deodorization, sterilization, and decolorization, displays an activity of decomposing ozone, and retains stability of quality for a long time.
Another object of this invention is to provide a catalyst for use in water treatment which displays a high ozone-decomposing activity, retains stability of quality for a long time, and permits the residual dissolved ozone in water to be decomposed and removed in a wide pH range.
A further object of this invention is to provide a method for the treatment of water by the use of ozone such as for deodorization, sterilization, and decolorization.
Yet another object of this invention is to provide a method for the decomposition and removal of dissolved ozone remaining in water after the water treatment by the use of ozone.